The present invention relates to an antenna having two crossed cylindro-parabolic reflectors with polarization rotation, for transmitting and/or receiving microwaves. It also relates to a process for manufacturing this antenna.
In some applications, it is necessary to have antennae in which the width (at half power) of the radiated beam is not identical in elevation and in bearing. For example, for a tracking antenna capable of tracking a target flying a low altitude, a maximum beam width in bearing is required for a minimum width in elvevation, so as to avoid parasitic reflections from the ground.
To obtain such an antenna, called a dissymmetric antenna, it is possible to use a microwave source emitting a beam whose width is different in the elvational and bearing directions. However, such a source proves to have poorer characteristics than a symmetrical source.
More particualalry, in such a source, the phase centers are different in elevation plane and in bearing plane. Further, for each of them, its locations varies with the frequency of the emitted microwave. The effect is a defocusing of the beam and thus, and increasing of the sidelobes of the radar pattern, which is a well known drawback. More generally, the more different is the radiated pattern of the source in elevation plane from what it is in bearing plane, the less constant with frequency the characteristics of the source. The result is that these dissymetric antennae are limited in relation with the bandwidth and/or the ratio of the widths of the beams in elevation plane and in bearing plane.